Added support in MockFileInfo for both get and set of properties including:
CreationTime, CreationTimeUtc,
LastAccessTime, LastAccessTimeUtc,
LastWriteTime, LastWriteTimeUtc,
IsReadOnly.

Encrypt and Decrypt will now respond by internally performing a XOR across the byte array.

OpenWrite and AppendText now work.

NOTE: No attempt is currently made to insure a file marked read only file is not written to.

Tests added to cover these new features.
MockFileStream supports append (defaults to no append)
Add XFS support to new tests